Couldn't connect to Server

// Program : GPRS Packet fetching and saved it into Database
// Author : Himachandra C

import java.io.*;
import java.net.*;
import java.sql.*;

class TCPServer
{
   public static void main(String argv[]) throws Exception
      {
         String clientSentence;
		 String Str1 = "$S";
		 String Str2;
         String capitalizedSentence;
         ServerSocket welcomeSocket = new ServerSocket(6789);
		 Connection con = null;
		 String url = "jdbc:mysql://localhost:3306/";
		 String db = "testserver";
		 String driver = "com.mysql.jdbc.Driver";
		 
		 try
		 {
		 
         while(true)
         {
            Socket connectionSocket = welcomeSocket.accept();
			
			System.out.println("Connection received from ::: " + connectionSocket.getInetAddress().getHostName());
            BufferedReader inFromClient = new BufferedReader(new InputStreamReader(connectionSocket.getInputStream()));
            DataOutputStream outToClient = new DataOutputStream(connectionSocket.getOutputStream());
            clientSentence = inFromClient.readLine();
            System.out.println("Received: " + clientSentence);
            capitalizedSentence = clientSentence.toUpperCase() + '\r' + '\n';
            outToClient.writeBytes("From Server :: " + capitalizedSentence);
			Str2 = clientSentence.substring(0,2);
			System.out.println("First two chars of string::" + Str2 + "Our defined String::" + Str1);
			if (Str1.equals(Str2))
			{
				System.out.println("The data is valid");
				outToClient.writeBytes("From Server :: Valid Data" );
				Class.forName(driver);
				con = DriverManager.getConnection(url + db,"root","root");
				Statement st = con.createStatement();
				String sql = "INSERT INTO DataReceived(ReceivedData) " +
                   "VALUES ('"+clientSentence+"')";
				try{
					
					int val = st.executeUpdate(sql);
					System.out.println("1 row affected");
				}
				catch (SQLException s){
					System.out.println("SQL statement is not executed!");
				}
			}
				else
			{
				System.out.println("The incoming data is Invalid");
				outToClient.writeBytes("From Server :: InValid Data" );
			}
         }
		 }
		 catch (Exception ex)
		 {
			 System.out.print("Whoops! It didn't work!\n");
		 }
      }
}